CopterSimulator/Unity/Assets/Scripts/AdvancedGizmo.cs

using UnityEngine;
using System.Collections;

public static class AdvancedGizmo {

	public enum CircleCloseType{
		None, 
		Direct,
		ToCenter
	}

	public static void Circle(float radius, float angle = 360.0f, int tesselation = 12, CircleCloseType close = CircleCloseType.None, Matrix4x4? transform = null){
		var matrixBackup = Gizmos.matrix;
		Gizmos.matrix = transform.HasValue ? transform.Value : Matrix4x4.identity;
	
		for (int i = 0; i < tesselation; ++i) {
			float angle0 = i * (angle * Mathf.Deg2Rad / tesselation);
			float angle1 = (i + 1) * (angle * Mathf.Deg2Rad / tesselation);

			var p0 = new Vector3(Mathf.Sin(angle0) * radius, 0, Mathf.Cos(angle0) * radius);
			var p1 = new Vector3(Mathf.Sin(angle1) * radius, 0, Mathf.Cos(angle1) * radius);

			Gizmos.DrawLine(p0, p1);
		}

		if (close != CircleCloseType.None) {
			float angle1 = angle * Mathf.Deg2Rad;
			var p0 = new Vector3(Mathf.Sin(0) * radius, 0, Mathf.Cos(0) * radius);
			var p1 = new Vector3(Mathf.Sin(angle1) * radius, 0, Mathf.Cos(angle1) * radius);

			if(close == CircleCloseType.Direct){
				Gizmos.DrawLine(p0, p1);
			}else{
				Gizmos.DrawLine(p0, Vector3.zero);
				Gizmos.DrawLine(p1, Vector3.zero);
			}
		}
		Gizmos.matrix = matrixBackup;
	}

	public static void CircleArrow(float radius, float angle = 360.0f, int tesselation = 12,  CircleCloseType close = CircleCloseType.None, Matrix4x4? transform = null){
		Circle(radius, angle, tesselation, close, transform);
		float len = 0.03f;
		float wid = 0.01f;
		float angleOffset = 2.0f * Mathf.Asin (len / (2.0f * radius)) * Mathf.Sign(angle);

		var matrixBackup = Gizmos.matrix;
		Gizmos.matrix = transform.HasValue ? transform.Value : Matrix4x4.identity;

		var radiusVector = new Vector3(Mathf.Sin(0), 0, Mathf.Cos(0));

		var p1 = new Vector3(Mathf.Sin(angleOffset), 0, Mathf.Cos(angleOffset)) * radius;
		var p0 = radiusVector * radius;

		var dir = (p1 - p0).normalized;
		var dir2 = Vector3.Cross (dir, Vector3.up).normalized;

		Gizmos.DrawLine(p0, p1 + dir2 * wid);
		Gizmos.DrawLine(p0, p1 - dir2 * wid);
		Gizmos.DrawLine(p1 + dir2 * wid, p1 - dir2 * wid);

		Gizmos.matrix = matrixBackup;
	}
}